Aorta and Its Branches

Aorta and Its Branches

The aorta is the body’s largest artery and emerges from the left ventricle of the heart. Its walls are approx-imately 2 mm in thickness, and its internal diameter is 2.5 cm. Backflow of blood during diastole is prevented by the aortic valve, at the base of the aorta. An aorticsinus opposes each cusp of the aortic valve. Each aor-tic sinus contains baroreceptors required for reflex regulation of blood pressure. The aorta consists of four portions: the ascending aorta, aortic arch, descending aorta, and abdominal aorta.

■■ The first portion of the aorta is the ascending aorta. It runs posteriorly and to the right of the pulmonary trunk for a short length of only 5 cm before it curves to the left as the aortic arch. The right and left coronary arteries are the only branches of the ascending aorta. They supply the myocardium with blood.

■■ The aortic arch curves across the superior surface of the heart and is deep to the sternum. It begins at the sternal angle, at the T4 level. The aortic arch connects the ascending aorta with the descending aorta. Three arteries originate along the aortic arch that deliver blood to the head, neck, shoulders, and upper limbs:

 • The brachiocephalic trunk: Superior, under the right sternoclavicular joint, it branches after a short distance into the right common carotid artery and right subclavian artery. The brachiocephalic trunk is also known as the innominate artery. There are three primary branches from each subclavian artery before it leaves the thoracic cavity: the internal thoracic artery, vertebral artery, and thyrocervical trunk.

 • The left common carotid artery

 • The left subclavian artery

■■ The descending aorta is continuous with the aortic arch. It runs along the anterior spine. The diaphragm divides the descending aorta into a superior thoracic aorta, from T5 to T12, and an inferior abdominal aorta. The branches of the thoracic aorta are the bronchial, pericardial, esophageal, mediastinal, and intercostal arteries.

■■ The abdominal aorta, beginning immediately inferior to the diaphragm, is a continuation of the thoracic aorta. It delivers blood to the abdominopelvic organs and structures, run-ning to the L4 level. Its major branches to the visceral organs are not paired. The branchesarise on the anterior surface of the abdominal aorta, extending into the mesenteries. Unpaired branches in the abdomen include the celiactrunk and the superior and inferior mesen-teric arteries. The celiac trunk supplies blood to the liver, stomach, and spleen. The superior mesenteric artery arises approximately 2.5 cm inferior to the celiac trunk and supplies the arteries of the pancreas, small intestine, and right and middle parts of the large intestine. The inferior mesenteric artery supplies blood to the terminal portions of the colon, which include the left large intestine, sigmoid colon, and rectum. The inferior phrenic arteries supply the inferior diaphragm surface and infe-rior esophagus. The adrenal arteries, which originate on either side of the aorta, near the bottom of the superior mesenteric artery, supply the adrenal glands. The renal arteries arise just inferior to the superior mesenteric artery, trav-eling posterior to the peritoneal lining to reach the adrenal glands and kidneys. The gonadalarteries begin between the mesenteric arteries and are called the testicular arteries in males and the ovarian arteries in females. The small lumbar arteries arise on the aorta’s posteriorsurface to supply the spinal cord, vertebra, and abdominal wall. The abdominal aorta divides into the right and left common iliac arteries.

TABLE 19-2 summarizes the major branches ofthe aorta.

Head and Neck Arteries

The head and neck are supplied by four paired arter-ies: the common carotid arteries plus three branches from each subclavian artery, the vertebral arteries, thyrocervical trunks, and costocervical trunks. Thecommon carotid arteries have the largest blood dis-tribution, with each being divided into two primary branches: the internal and external carotid arteries. A slight dilation of the internal carotid artery, known as the carotid sinus, is located at the division point. In the carotid sinus are baroreceptors that help to control blood pressure. Chemoreceptors involved in the control of respiration are nearby and are known as the carotid bodies. Pressure applied to the neck, near the carotid sinuses, can cause unconscious-ness because this increases blood pressure, lead-ing to vasodilation and impaired blood delivery to the brain.

Common Carotid Arteries

The right common carotid artery arises from the brachiocephalic trunk, whereas the left common carotid artery is the second branch of the aortic arch (FIGURE­19- 9). Both arteries ascend through the lateral neck. At the level of the Adam’s apple, they divide into their primary branches: the external and internal carotid arteries. Most of the head, except for the brain and orbits, is supplied by the external carotid arteries. Each of these arteries runs superi-orly. Its branches include

■■ Superior thyroid artery:supplying the thyroid gland and larynx

■■ Lingual artery:supplying the tongue

■■ Facial artery:supplying the skin and anterior face muscles

■■ Occipital artery:supplying the posterior scalp

Each of the external carotid arteries ends when they split into a superficial temporal artery and a maxillary artery. The superficial temporal artery supplies most of the scalp as well as the parotid sali-vary gland. The maxillary artery supplies both jaws, teeth, nasal cavity, and muscles used for chewing. The middle meningeal artery is a branch of the maxillary artery that enters the skull through the foramen spi-nosum. It supplies the inner parietal bone surface, squamous section of the temporal bone, and the dura mater underneath.

The orbits and more than 80% of the cerebrum are supplied by the larger internal carotid arteries. They run deeply, entering the skull through the tem-poral bones’ carotid canals. In the cranium, each of them branches into a primary ophthalmic artery and then into the anterior and middle cerebral arteries. The eyes, forehead, nose, and orbits are supplied by the ophthalmic arteries . The medial surface of the frontal and parietal lobes of the cerebral hemisphere are supplied by each anterior cerebral artery. This also anastomoses with its paired opposing artery via a short anterior communicating artery. The ­middle cerebral arteries supply the lateral sections of the frontal, parietal, and temporal lobes. These arteries run in the lateral sulci of each cerebral hemi-sphere. TABLE 19-3 summarizes the major branches of the carotid arteries.

Vertebral Arteries

At the root of the neck, the vertebral arteries emerge from the subclavian arteries, continuing through the foramina in the transverse processes of the cervical vertebra. They enter the skull via the foramen mag-num, branching to the vertebra, cervical spinal cord, and various deep neck structures. In the cranium, the basilar artery is formed by the joining of the left and right vertebral arteries. The basilar artery ascends along the brain stem’s anterior aspect and branches to the cerebellum, pons, and inner ear. It also divides, at the pons–midbrain border, into two posteriorcerebral arteries. These arteries supply the inferiorsections of the temporal lobes and the occipital lobes.

The posterior cerebral arteries are connected by the posterior communicating arteries to the ­middle cerebral arteries, anteriorly. There are two posterior and single anterior communicating arteries that continue the arterial anastomosis known as the cerebral­ arterial circle, which is also called thecircleof Willis. The circle of Willis encircles the optic chi-asma and pituitary gland. It joins the anterior and pos-terior blood supplies of the brain and balances blood pressure in these areas. It also provides alternative routes for blood to be able to reach the brain should occlusion of a vertebral or carotid artery occur.

Thyrocervical and Costocervical Trunks

The thyrocervical trunk and costocervical trunk are short vessels emerging from the subclavian artery, lateral­ to the vertebral arteries on both sides. The ­thyrocervical trunk primarily supplies the thyroid gland, parts of the cervical vertebra and spinal cord, and certain scapular muscles. The costocervical trunk supplies muscles of the deep neck and the superior intercostal muscles.

Upper Limb and Thoracic Arteries

The subclavian arteries branch to supply all portions of the upper limbs (FIGURE 19-10). First, they branch off to the neck but then run laterally to enter the axilla by moving between the clavicle and first rib on each side. At this point they are renamed as axillary arteries. The wall of the thorax is supplied by vessels from either the thoracic aorta or from subclavian artery branches. Small branches of the thoracic aorta supply most of the blood to the visceral thoracic organs.

Axillary Artery

Each axillary artery branches to the axilla, chest wall, and shoulder girdle. These axillary branches include the thoracoacromial, lateral thoracic, subscapular artery,and the anterior and posterior circumflex humeralarteries. Thethoracoacromial arterysupplies thepectoral region and deltoid muscle. The lateralthoracic artery supplies the breast and lateral chestwall. The subscapular artery supplies the dorsal tho-rax wall, the scapula, and a portion of the ­latissimus dorsi muscle. The anterior and posterior circumflex humeral arteries help to supply the deltoid muscle and shoulder joint. The axillary artery becomes the bra-chial artery as it emerges from the axilla.

Brachial Artery

The brachial artery supplies the anterior flexor arm muscles. A major branch is the deep artery of the arm, which serves the posterior triceps brachii muscle. Near the elbow, the brachial artery branches to con-tribute to an anastomosis that serves the elbow joint and connect­ it to the forearm arteries. Crossing the anterior midline aspect of the elbow, it provides the brachial pulse, which is easily palpated. Just beyond the elbow, it branches to form the radial and ulnar arteries. The brachial artery is an elastic artery.

Radial Artery

The radial artery proceeds from the cubital fossa’s median line, reaching the styloid process of the radius. It supplies the lateral forearm, wrist, thumb, and index finger muscles. At the thumb’s root it provides the radial pulse.

Ulnar Artery

The ulnar artery supplies the medial aspects of the forearm and index finger as well as the third, fourth, and fifth fingers. It gives off a short proximal branch known as the common interosseous artery, ­running between the radius and ulna, serving the forearm’s deep flexors and extensors. At the wrist both the ulnar and radial arteries fuse, forming the superfi-cial and deep palmar arches.

Palmar Arches

The superficial and deep palmar arches are formed by branches of the radial and ulnar arteries that anasto-mose in the palm. Blood supply to the fingers arises from the palmar arches, becoming the metacarpalarteries and digital arteries.

Internal Thoracic Arteries

The thoracic wall is supplied by the internal thoracicarteries as well as the posterior intercostal arteries and superior phrenic arteries. Formerly known as the internal­ mammary arteries, the internal thoracic arteries emergefrom the subclavian arteries. They supply blood to most of the thoracic wall. Each descends lateral to the sternum, branching to form the anterior intercostalarteries and supplying the intercostal spaces anteriorly.Superficial branches are also sent to the skin, mammary glands, anterior abdominal wall, and diaphragm.

Posterior Intercostal Arteries

The costocervical trunk branches to form the ­posterior two pairs of posterior intercostal arteries. Nine additional pairs arise from the thoracic aorta, anasto-mosing anteriorly with the anterior intercostal arter-ies. A pair of subcostal arteries arises from the thoracic aorta, inferior to the 12th rib. The posterior intercostal arteries supply the deep muscles of the back, the poste-rior intercostal spaces, the vertebra, and the spinal cord. The intercostal muscles are supplied by both the poste-rior and anterior intercostal arteries.

Superior Phrenic Arteries

The posterior superior diaphragm surface is served by either one or more paired superior phrenic arteries.

Thoracic Viscera Arteries

The arteries of the thoracic viscera include the pericar-dial, bronchial, esophageal, and mediastinal arteries. The tiny pericardial arteries supply the posterior pericardium. The two left and one right bronchialarteries supply oxygenated blood to the bronchi,lungs, and pleura. Four or five esophageal arteries supply the esophagus. The posterior mediastinum is served by the many small mediastinal arteries.

Abdominal Arteries

The abdominal aorta branches to form the abdominal arteries. Nearly half of all arterial flow moves through these vessels during rest. All of them are paired vessels except for the celiac trunk and the superior and inferior mesenteric arteries (FIGURE 19-11). The abdominal arter-ies supply the abdominal wall, diaphragm, and visceral organs inside the abdominopelvic cavity and include the inferior phrenic arteries, celiac trunk, superior mesenteric artery, suprarenal arteries, renal arteries, gonadal arter-ies, inferior mesenteric artery, lumbar arteries, median sacral artery, and common iliac arteries.

Inferior Phrenic Arteries

The inferior phrenic arteries serve the inferior dia-phragm surface, emerging from the aorta just inferior to the diaphragm at the T12 level.

Celiac Trunk

The celiac trunk consists of large, unpaired arteries from the abdominal aorta (FIGURE 19-12). This divides soon after emerging into the common hepatic, splenic, and leftgastric arteries. The common hepatic artery branchesto the stomach, pancreas, and duodenum. At the point where the gastroduodenal artery branches, the commonhepatic artery becomes the hepatic artery proper.This splits into the left and right branches serving the liver. The splenic artery branches to the pancreas and stomach as it passes deep to the stomach, terminating at the spleen. Part of the stomach and the inferior esoph-agus are supplied by the left gastric artery. The rightgastroepiploic artery branches from the gastroduodenalartery, whereas the left gastroepiploic artery branches from the splenic artery. Both serve the stomach’s greater curvature. The right gastric artery supplies the ­stomach’s lesser curvature. It may emerge from either the hepatic artery proper or the common hepatic artery.

Superior Mesenteric Artery

The superior mesenteric artery is large and unpaired, emerging from the abdominal aorta just below the celiac trunk and the L1 level. Running deep to the pancreas, it enters the mesentery, featuring many anastomosing branches serving almost all the small intestine, through the intestinal arteries. It also serves the appendix, cecum, and ascending colon via the ileocolic and right colic arteries. Additionally, the superior mesenteric artery services part of the trans-verse colon via the middle colic artery.

Suprarenal Arteries

Emerging from the abdominal aorta, the middlesuprarenal arteries flank the origin of the superiormesenteric artery. The adrenal or suprarenal glands above the kidneys are supplied with blood from these arteries. Two sets of branches, the superior suprarenalbranches, from the inferior phrenic arteries, and the inferior suprarenal branches, from the renal arteries,also supply the adrenal glands.

Renal Arteries

The right and left renal arteries are short in length but wide. They emerge from the lateral aortic surfaces just below the superior mesenteric artery between the L1 and L2 levels. Each renal artery serves the ­kidney on its side.

Gonadal Arteries

The two gonadal arteries have different names in either gender. In women they are known as the ovarian­arteries, whereas in men they are known as the­testicular arteries. The ovarian arteries serve part of the uterine tubes and the ovaries. They are much shorter than the testicular arteries, which descend to enter the scrotum and serve the testes.

Inferior Mesenteric Artery

The final major branch of the abdominal aorta is the single inferior mesenteric artery. It emerges from the anterior aorta at the L3 level. It supplies the distal large intestine, from the mid transverse colon to the mid rectum. The inferior mesenteric artery ­accomplishes this through its left colic, sigmoidal, and superior­ rectal branches. There are looped anastomoses­ between the superior and infe-rior mesenteric arteries, which help to move blood to the digestive viscera when there is trauma to one of these arteries.

Lumbar Arteries

Four pairs of lumbar arteries arise from the postero-lateral aortic surface in the lumbar area. They supply the posterior wall of the abdomen.

Median Sacral Artery

The single median sacral artery emerges from the pos-terior abdominal aorta’s surface at its terminus. This artery is very small and delivers blood to the sacrum and coccyx.

Common Iliac Arteries

The aorta splits into the right and left common iliacarteries at the L4 level. They deliver blood to the pelvicorgans, lower abdominal wall, and lower limbs.

Pelvic and Lower Limb Arteries

The common iliac arteries are divided into two major branches at the level of the sacroiliac joints: the inter-nal and external iliac arteries (FIGURE 19-13). Blood is distributed by the internal iliac arteries primarily to the pelvic region. The external iliac arteries mostly supply the lower limbs but also branch to the abdominal wall.

Internal Iliac Arteries

The two internal iliac arteries carry blood to the pelvic walls, bladder, rectum, and specific organs in either gen-der. In females these organs are the uterus and vagina, whereas in males they are the prostate and ductus defer-ens. The internal iliac arteries also use the superior andinferior gluteal arteriesto serve the gluteal muscles,the obturator artery to serve the adductor muscles of the medial thigh, and the ­internal pudendal artery to serve the external genitalia and perineum.

External Iliac Arteries

The external iliac arteries supply the lower limbs, branching also to the anterior abdominal wall. They pass under the inguinal ligaments, enter the thigh, and eventually become the femoral arteries.

Femoral Arteries

Each femoral artery passes down the anteromedial thigh to branch to the thigh muscles. Of the deep branches, the largest is called the deep artery of the thigh or deep femoralartery. It is the primary supplier of blood to the ham-strings, adductors, and quadriceps of the thigh. Proximal branches from the deep femoral artery are known as the lateral and medial circumflex femoral arteries. They encircle the neck of the femur, with the medial supply­ the knee area. It then splits into the anterior and posterior tibial arteries.

Anterior Tibial Artery

The anterior tibial artery courses through the ante-rior leg compartment, supplying the extensor mus-cles. It becomes the dorsalis pedis artery at the ankle, supplying the ankle and the dorsum of the foot. Another branch, the arcuate artery, links the dorsal metatarsal arteries to the metatarsus of the foot. The dorsalis pedis’ superficial portion ends as it penetrates the sole, forming the medial plantar arch. This artery provides the pedal pulse, which can be felt to assess blood supply to the leg.

Posterior Tibial Artery

The large posterior tibial artery moves through the posteromedial leg to supply the flexor muscles. It gives off a large branch proximally, known as the fibular (peroneal) artery. This artery supplies the lateral fibularis muscles. At the medial side of the foot, the artery divides into lateral and medial plantar arteries. These serve the plantar foot surface. The lateral end of the plantar arch is formed by the lateral plantar artery. From the plantar arch arise the plantar metatarsal arteries and digital arteries to the toes.

1. Name the largest diameter artery in the body, and describe its location.

2. Which arteries supply the larynx, tongue, meninges, and teeth with blood?

3. What is the circle of Willis?

4. Name unpaired arteries that branch from the abdominal aorta.

5. Which artery forms the radial and ulnar arteries?

6. Which artery is the largest in the lower limb?